Combination of response adapting filter and detector

ABSTRACT

A combination of a response adapting filter ( 11, 12, 13 ) and a detector ( 14 ), the detector having a predetermined spectral response function to electromagnetic radiation, a method of its preparation, a camera ( 11, 12, 13, 14, 15 ) comprising such a response filter and detector combination, and use thereof in e.g. colour measurements in combination with an integrating cavity and a vision inspection system of natural and/or a synthetic material surfaces; also a display and detector combination, a method of displaying optical information, a colour display and monitor system, and a method of controlling colour display, said combination, systems and methods comprising such combination of a response adapting filter and a detector.

1. BACKGROUND OF THE INVENTION

The present invention relates to combination of a response adaptingfilter and a detector, the detector having a predetermined spectralresponse function to electromagnetic radiation; a method of ispreparation, a camera comprising such a response filter and detectorcombination, and use thereof in e.g. colour measurements in combinationwith an integrating cavity and a vision inspection system of naturaland/or a synthetic material surfaces; also a display and detectorcombination, a method of displaying optical information, a colourdisplay and monitor system, and a method of controlling colour display,said combination, systems and methods comprising such combination of aresponse adapting filter and a detector.

The Technical Field

Basics for Colour Measurements

The standard 2° calorimetric observer was defined by CIE in 1931 throughthe colour matching functions {overscore (x)}(λ),{overscore (y)}(λ) and{overscore (z)}(λ). See CIE publication No 15, COLORIMETRY Officialrecommendation of the international commission on illumination, 1971.The tristimulus values, X, Y and Z, of a given colour stimulus of alight source S(λ) are defined and calculated or measured as:$\begin{matrix}{X = {k \times {\int_{\lambda\quad 1}^{\lambda\quad 2}{{\phi(\lambda)} \times {\overset{\_}{x}(\lambda)}{\mathbb{d}\lambda}}}}} & (1) \\{Y = {k \times {\int_{\lambda\quad 1}^{\lambda\quad 2}{{\phi(\lambda)} \times {\overset{\_}{y}(\lambda)}{\mathbb{d}\lambda}}}}} & (2) \\{Z = {k \times {\int_{\lambda\quad 1}^{\lambda\quad 2}{{\phi(\lambda)} \times {\overset{\_}{z}(\lambda)}{\mathbb{d}\lambda}}}}} & (3)\end{matrix}$wherein k is a factor for normalizing the light source, S(λ) defined as:$\begin{matrix}{k = \frac{100}{\int_{\lambda\quad 1}^{\lambda\quad 2}{{S(\lambda)} \times {\overset{\_}{y}(\lambda)}{\mathbb{d}\lambda}}}} & (4)\end{matrix}$and wherein φ(λ) is the colour stimulus in question defined as eitherfollowing formulas 5a, 5b and 5c:φ(α)=S(λ)×ρ(λ)   (5a)φ(λ)=S(λ)×β(λ)   (5b)φ(α)=S(λ)×τ(λ)   (5c)wherein

-   -   ρ(λ) is used when the colour stimulus in question concerns        reflectance of a sample,    -   β(λ) is used when the colour stimulus in question concerns        luminance factor of a sample    -   τ(λ) is used when the colour stimulus in question concerns        transmittance of a sample.

For the above-given definitions of k in formula (4), Y defines thereflectance, the luminance factor, or the transmittance, expressed inpercentage.

If the colour stimuli is direct light from the light source thenφ(λ)=S(λ) (and if given in Watts) and k=683 lumen×W⁻¹, then theY-stimulus value is the luminous flux from the light source.

The chromatic coordinates x,y are calculated from the tristimulus valuesas: $\begin{matrix}{\begin{bmatrix}x \\y\end{bmatrix} = \begin{bmatrix}\frac{X}{X + Y + Z} \\\frac{Y}{X + Y + Z}\end{bmatrix}} & (6)\end{matrix}$

Hence, for a given light source S(λ), the colour is unambiguously givenby the chromatic co-ordinates (x,y) and Y. Other chromatic coordinatesand colour differences defined by CIE as well as defined by others canalso be derived from the tristimulus values X, Y and Z, of the CIErecommendations, ibid.

Colour Measurements

The function φ(λ) can be measured with a colour measuring systemcomprising a simple sensor, a scanning monochromator and a suitablelight source and the tristimulus values X, Y and Z can be derivedaccording to formulas (1), (2) and (3) and tabulated values of{overscore (x)}(λ), {overscore (y)}(λ) and {overscore (z)}(λ).

Most spectroradiometers utilizes this principle, although withsubstantially modified equipment. Preferably an imaging sensor like aCCD or a CMOS array photo detector is used as the sensor.

Alternatively, a grating, a linear CCD, or an array of photodiodes canbe used to simultaneously measure φ(λ).

Measurements with spectroradiometers and uniform illumination can bycalibration to a known sample be made independent of the light sourceused. Consequently, such measurements can be converted to a result forany given light source provided that the object measured is uniformlyilluminated during the measurement.

Some spectroradiometers uses a number of LED's with dominant wavelengthsthroughout the spectrum instead of a ‘white’ light source and amonochromator. Such spectroradiometers work fine on non-fluorescentobjects.

A simple calorimeter comprises a X-filter, a Y-filter and a Z-filter incombination with an imaging device and a sensor, each of said X, Y,Z-filters realizing one of the colour-matching functions {overscore(x)}(λ), {overscore (y)}(λ) and {overscore (z)}(λ). Known filterscomprise a stack of colour filters, a mosaic of filter segments, and atemplate with a grating.

Only stacked colour filters in combination with an imaging sensorexhibit imaging properties.

The filters can be positioned in the colour measuring system to eithershape the light source or shape the incoming light. Both methods areused in various applications. In many cases, because sensors are smalland light sources in many cases are relatively large, the filters arepositioned to shape the incoming light in front of the sensor.

Measurements with prior art filter calorimeters must be performed with agiven light source the result of which, however, cannot unambiguously beconverted from this one light source to another, even if proper uniformillumination has been used.

Prior art filter colorimeters suffers from either poor match to thecolour-matching functions or low transmittance in case of the stackedtype filter.

Stacked type filters can be made imaging, however they suffer a limitedaccuracy, and they require very expensive detectors such as cooled CCD'sin order to operate under the inherently low transmittance of thesefilters. Mosaic- and template-type filters cannot be made imaging.Consequently, there is a need for colour measuring systems comprisingcolour-matching filters and detector combinations which allow imagingand which does not require expensive sensitive and cooled detectors.

Many attempts have been made to establish colour-measuring systems anddevices, including calibration procedures therefore.

Colour cameras comprising 3 CCD detectors where the incoming light issplit into 3 components of red, green and blue light have beensuggested. However, shades of these three colours cannot bedistinguished from a change in luminance because only one channelresponds to the shades. Colour-measuring systems and devices based onsuch light splitting function cannot perform repeatable and traceablecolour measurements according to the standards set by CIE.

Illumination and Geometry in Colour Measurements

Standard geometry's are defined for measuring reflectance and/ortransmittance of an object, cf. CIE publication No 38 ‘Radiometric andphotometric characteristics of materials and their measurement’, 1977.The standard geometries are 0°/45°, 0°/diffuse and 0°/total. The 0°measurements are performed in integrating spheres thereby obtaininguniform and diffuse illumination, and simultaneously excluding exteriorlight. The diffused light is obtained by including a light trap for thespecular component.

According to Helmholtz reversal principle, the direction of illuminationand observation can be reversed. Prior art measurements set-ups are welldescribed in G. Wyszecki, “COLOR SCIENCE Concepts and Methods,Quantitative Data and Formulae”, 1982, in 3.3.7 “Standard Illuminatingand viewing conditions” and in 3.12.3 “Spectrometers”.

Calibration of Calorimeters

For filter colorimeters comprising filters exhibiting given colourmatching functions that are not identically with the CIE colour matchingfunctions, the tristimulus values X′, Y′ and Z′ are found for a givencolour stimulus. The colorimeter response might be improved in a more orless limited region of the colour space by introducing a 3×3-correctionmatrix M_(correction) as defined in formula (7). This matrix is found bymeasuring, at least 3, known samples, and then solving a set ofequations to find the correction matrix. $\begin{matrix}{\begin{bmatrix}\begin{matrix}X \\Y\end{matrix} \\Z\end{bmatrix} = {M_{correction} \times \begin{bmatrix}\begin{matrix}X^{\prime} \\Y^{\prime}\end{matrix} \\Z^{\prime}\end{bmatrix}}} & (7)\end{matrix}$

In the extreme case, the response of special samples, monochromaticradiation can be measured for many given wavelengths, and a correctionmatrix can be found by minimizing with respect to some suitable errormetrics, e.g. the f′₁ defined in the following section.

Calculation of f′₁ Errors for Detectors with Specified SpectralResponsivity

In CIE publication No 53, “Methods of characterising the performance ofradiometers and photometers”, 1982, metrics are given for integratedphotometer errors.

This error metrics concerns only the relative response. The output fromradiometers and photometers must be corrected for linearity and darkcurrent according to well-known procedures. $\begin{matrix}{f_{1}^{\prime} = {\frac{\int_{\lambda\quad 1}^{\lambda\quad 2}{{{{S_{\chi}(\lambda)}_{rel} - {S_{T}(\lambda)}_{rel}}}{\mathbb{d}\lambda}}}{\int_{\lambda\quad 1}^{\lambda\quad 2}{{S_{T}(\lambda)}_{rel}{\mathbb{d}\lambda}}}\quad{wherein}}} & (8) \\{{S_{\chi}(\lambda)}_{rel} = \frac{\int_{\lambda\quad 1}^{\lambda\quad 2}{{S(\lambda)}_{A} \times {S_{T}(\lambda)}_{rel}{\mathbb{d}\lambda}}}{\int_{\lambda\quad 1}^{\lambda\quad 2}{{S(\lambda)}_{A} \times (\lambda)_{rel}{\mathbb{d}\lambda}}}} & (9)\end{matrix}$and

-   -   S_(T)(λ)_(rel): Specified relative responsivity    -   S(λ)_(rel): Relative photometer responsivity    -   S(λ)_(A): Relative spectral distribution of CIE standard        Illuminant A

In the case of a calorimeter, 3 separate detectors are used; one foreach colour-matching function, and hence 3 f′₁ errors are obtained.

Prior Art Disclosures

G. Wyszecki, “COLOR SCIENCE Concepts and Methods, Quantitative Data andFormulae”, 1982, 3.12.5 “Tri-stimulus-Filter Colorimeters”, describesthe different types of calorimeters, including the template type, thestacked filter type, and the mosaic filter type. The template type andmosaic filter type can be very accurate but cannot be imaging. Thestacked filter type can be accurate but with the expense of very smalltransmittance and therefore only useful with very sensitive sensors e.g.cooled CCD or photo multipliers.

U.S. Pat. No. 5,850,472 “Colorimetric imaging system for measuring colorand appearance” discloses an imaging calorimeter based on a colour videocamera with RGB response. In the “real world” the transform from RGB toXYZ colours in CIE space is not possible.

2. DISCLOSURE OF THE INVENTION

Object of the Invention

It is an object of the present invention to seek to provide an improvedcolour measuring system, in particular a tristimulus camera.

It is another object of the present invention to seek to provide acolour measuring system with improved transmittance.

It is another object of the present invention to seek to provide acolour measuring system comprising colour-matching filters and detectorcombinations which allow imaging and which does not require expensivesensitive and cooled detectors.

Further objects appear from the description elsewhere.

Solution According to the Invention

“Combination of Response Adapting Filter and Detector”

In an aspect according to the present invention, there is provided acombination of a response adapting filter and a detector, the detectorhaving a predetermined spectral response function D(λ) toelectromagnetic radiation; the response adapting filter comprising:

-   -   one or more optical multilayered structures of thin films on a        substrate, said optical multilayer structures comprising two or        more layers of thin film materials, said thin film materials        comprising dielectric materials, metallic materials, or a        combination thereof; and    -   said layers of thin films being adapted to provide a spectral        transmittance T(λ) so that the spectral response D(λ)T(λ) of the        detector matches a predetermined spectral-matching function        y(λ).

It has surprisingly turned out that a very high transmittance isachieved whereby it is obtained that a colour measuring systemcomprising colour matching filters and detector combinations that allowimaging and which does not require expensive sensitive and cooleddetectors can be provided.

Preferred embodiments are defined in the dependent claims 2-6.

“Method of Preparing a Response Adapting Filter and DetectorCombination”

In another aspect according to the present invention there is provided amethod of preparing a response adapting filter and detector combination,the method comprising:

-   -   providing a detector, said detector having a pre-determined        spectral response function D(λ);    -   providing a substrate;    -   providing an optical multilayered structure on said substrate;        said optical multilayered structure comprising two or more        layers of thin film materials, said thin film materials        comprising dielectric materials, metallic materials, or a        combination thereof;    -   said optical multilayered structure of thin films being adapted        to provide a spectral transmittance T(λ) according to an aspect        of the invention for a combination of a response adapting filter        comprising said optical multilayered structure of thin films and        a detector;    -   said two or more layers of thin film materials being provided by        deposition of said thin film materials by reactive gas        deposition, and    -   said deposition being controlled by optical measurements;    -   whereby it is obtained that a colour measuring system comprising        colour-matching filters and detector combinations which allow        imaging and which does not require expensive sensitive and        cooled detectors can be provided.

Preferred embodiments are defined in the dependent claims 8-11.

“Camera”

In still another aspect according to the present invention, there isprovided a camera, the camera comprising:

-   -   an aperture means adapted to control radiant power from an        object; p1 one or more response adapting filters according to an        aspect of the invention, or obtainable by the method according        to another aspect of the invention;    -   an imaging means adapted to generate an image of said radiant        power of said object; said imaging means having an imaging        spectral transmittance L(λ) and being positioned so that said        one or more response adapting filters lie in the object space        thereof, and    -   one or more energy collecting and detecting means adapted to        collect and detect radiant power in discrete points of said        image, said energy collecting means having an image collecting        spectral response D(λ) which is substantially similar for all        said discrete points of said image, said one or more response        adapting filter being positioned in the object space of said        imaging means;    -   whereby it is obtained that a colour measuring system, in        particular a tristimulus camera, comprising colour-matching        filters and detector combinations which allow imaging and which        does not require expensive sensitive and cooled detectors can be        provided.

Preferred embodiments are defined in the dependent claims 13-19.

“Camera Applications”

In still a further aspect according to the present invention, there isprovided use of a camera according to the present invention. Preferreduses are defined in claims 20-24.

In a preferred embodiment a camera according to the invention is used incombination with an integrating cavity.

In another preferred embodiment a camera according to the invention isused in colour measurement in a vision inspection system.

In another preferred embodiment a camera according to the invention isused in colour measurement of a surface of natural and/or a syntheticmaterial, wherein said natural surface is selected from the groupconsisting of a surface of a biological material including human andanimal tissue and skin; and plants tissue including wood, and whereinsaid synthetic natural surface is selected from the group consisting ofa surface of a material of textile, concrete, and paint.

“Display and Detector Combination”

In another aspect according to the present invention, there is provideda display and detector combination, said combination comprising:

-   -   a combination of a response adapting filter and a detector        according to the invention, said combination producing a        detector signal in response to electro-magnetic radiation; and    -   a display means, said display means comprising light emitting        means to emit light in response to said detector signal, whereby        optical information, e.g. tristimulus values of colour        measurements can be displayed, e.g. on a video display unit,        whereby an optimized reproduction of the object/scene can be        obtained on said display means.

Preferred embodiments are defined in claims 26-29.

“Method of Displaying Optical Information”

In another aspect according to the present invention, there is provideda method of displaying optical information, said method comprising:

-   -   producing a detector signal in response to electro-magnetic        radiation, said detector signal being produced by a combination        of a response adapting filter and a detector according to an        aspect the present invention; and    -   producing a display on a display means, said display means        comprising light emitting means emitting light in response to        said detector signal.

Preferred embodiments are defined in claims 31-32.

“Colour Display and Monitor System”

In another aspect according to the present invention, there is provideda colour display and monitor system, said display and monitor systemcomprising:

-   -   a colour display means, said colour display means comprising        light-emitting means to emit coloured light in response to a        display control signal; and    -   a monitor means, said monitor means comprising a combination of        a response adapting filter and a detector as defined in an        aspect of the present invention, said monitor means producing a        monitor signal in response to said emitted light of said colour        display means, whereby a colour display means displaying optical        information, e.g. screen of in a video display system displaying        a colour, or an image, can be monitored with a detector having a        predetermined spectral detector response and provide a monitor        signal which can be used to adjust the display control signal of        the colour display. In this way colour information of e.g. a        screen of video display unit, a projector screen, or a print        produced by a printer, can be monitored and the display control        signal can be adjusted to provide a desired display, e.g.        correcting the displayed colour, intensity, etc.

It is intended that the term “light-emitting means to emit colouredlight” include a colour light source, e.g. a phosphorous materialemitting coloured light, or e.g. a diffusor emitting transmitted orreflected light, or fluorescence light.

Also, it is intended that the term “a display control signal” includescontrol signal for any suitable display means, e.g. control signals foran electronic monitor screen device, or e.g. control signals for acolour printer, said control signals optionally triggering furthercontrol signals of said means and devices.

Preferred embodiments are defined in claims 34-41.

In a preferred embodiment, said system further comprising signal storagemeans, said signal storage means storing at least one reference displaycontrol signal whereby it is obtained that a reference point for thedisplay can be established.

In a preferred embodiment, said at least one reference display controlsignal is derived from a detector signal generated by a display anddetector combination as defined in an aspect of the invention wherebye.g. electronic information of a colour display provided by a detectorhaving a predetermined spectral detector response can be obtained.

In another preferred embodiment, said at least one reference displaycontrol signal is derived from said monitor signal whereby e.g. areference point and a possible drift therefrom by the displayed colourdisplay can be monitored.

In a preferred embodiment, said system further comprising a signalcomparator means for comparing said monitor signal and said at least onereference display control signal, said signal comparator means producinga comparator control signal in response thereto whereby e.g. a possibledrift from a reference point can be established.

Generally, a comparator control signal can be used for variousapplications, e.g. providing a feedback to illumination means for acorrected illumination of an object being measured.

In a preferred embodiment said system further comprising a control meansfor adjusting said display control signal, said control means adjustingsaid display control signal in response to said comparator controlsignal whereby the display can adjusted to a predetermined spectraldetector response of the monitor and matching a predeterminedspectral-matching function, e.g. that of a CIE standard calorimetricobserver.

In a preferred embodiment, said display control signal, said monitorsignal, said at least one reference display control signal, or acombination thereof, comprises an electronic tristimulus signal, inparticular that of a CIE standard calorimetric observer.

The display means can be any suitable display means for displayingoptical colour information.

In a preferred embodiment, said display means comprises a display meanssuch as an electronic display screen, preferably a video display unit; aprojector screen system, or an electronic printer, preferably a colourprinter.

Generally, connection between said colour display means and monitormeans include any suitable signal connecting means known to a skilledperson.

In a preferred embodiment, colour display and monitor system furthercomprises a connection means for connecting said monitor signal to adisplay and detector combination as defined in an aspect of theinvention, in particular a display means such as an electronic displayscreen, preferably a video display unit; a projector screen system, oran electronic printer, preferably a colour printer.

“Method of Controlling a Colour Display”

In another aspect according to the present invention, there is provideda method of controlling a colour display, said method comprising:

-   -   displaying a colour on a display means, said display means        comprising light emitting means to emit coloured light in        response to a display control signal;    -   monitoring said display means by a monitor means comprising a        combination of a response adapting filter and a detector as        defined in an aspect of the present invention, said monitor        means producing a monitor signal in response to said emitted        light of said display means;    -   comparing said at least one reference control signal and said        monitor signal by comparator means for comparing said at least        one reference control signal and said monitor signal, said        comparator means producing a comparator control signal in        response thereto; and    -   adjusting said display control signal by a control means for        adjusting said display control signal, said control means        adjusting said display control signal to produce an adjusted        response of said emitted coloured light on said display means.

In a preferred embodiment, said display control signal, said monitorsignal, said at least one reference display control signal, or acombination thereof, comprises an electronic tristimulus signal wherebyin particular an optimized reproduction of a scene on said display meanscan be obtained.

It should be noted however that the term “light-emitting means to emitcoloured light” is intended to have a broad meaning, including a colourlight source, e.g. a phosphorous material emitting coloured light, ore.g. a diffusor emitting transmitted or reflected light, or fluorescencelight. However, the term is also intended to include e.g. a colour printthe colour of which may be controlled by adjusting the printer producingsuch a colour print by a signal derived from said monitor signal.

3. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, by way of examples only, the invention is furtherdisclosed with detailed description of preferred embodiments. Referenceis made to the drawings in which

FIG. 1 shows an embodiment of the present invention illustrating atristimulus filter-type imaging camera according to the invention, wherethe three filters are mounted in a filter-wheel or filter sledge andimages are detected by one array detector;

FIG. 2 shows an alternative embodiment of a tristimulus filter-typeimaging camera in which three separate channels each having it own arraydetector are used;

FIGS. 3 and 4 show alternative embodiments of the present inventionshown in FIG. 1 and FIG. 2;

FIGS. 5A and 5B show alternative embodiments of an optical multilayerstructure of thin films for a colorimeter and tristimulus camera withhigh transmittance;

FIG. 6 illustrates the response folding operation for achieving filtercharacteristics of CIE colour-matching functions;

FIG. 7 shows a tristimulus filter design by both stacking andside-by-side placement of coloured filters for colorimeters of thenon-imaging type;

FIG. 8 shows a template for the template type colorimeter of thenon-imaging type according to prior art;

FIG. 9 shows a pixel layout on a CCD chip used for colour photographywith one CCD according to prior art;

FIG. 10 shows a layout used for colour photography with 3 CCD camerasaccording to prior art;

FIG. 11 shows a spectral response of RGB type CCD cameras according toprior art as used in FIG. 9 and 10;

FIG. 12 shows a tristimulus filter design comprising a stack of colouredfilters for calorimeters and tri-stimulus cameras with very lowtransmittance and medium match;

FIG. 13 shows a detailed illustration of an embodiment of a cameracomprising of a front lens group, next to the filters, spacing with anaperture and a rear lens group next to the image collecting means;

FIG. 14 shows measured system responses of an embodiment of a cameracompared with CIE responses;

FIG. 15 shows a cross-sectional sketch of an integrating cavity to beused in combination with a camera according to the invention (notshown);

FIG. 16 shows an embodiment of a camera recording an image of a scene,and storing one or more signals representing said image;

FIG. 17 shows an embodiment of a display and detector combination, herea camera recording and storing an image as shown in FIG. 16, anddisplaying said image, optionally said stored image, on a display;

FIG. 18 shows an embodiment of a colour display and monitor system formonitoring a colour display and optionally correcting, or calibratingsaid displayed colour display; and

FIG. 19A and 19B show an embodiment of a colour display and monitorsystem incorporated in a display and detector combination as shown inFIG. 17.

4. DETAILED DESCRIPTION

FIG. 1 shows an embodiment of the present invention illustrating atristimulus filter-type imaging camera according to the invention, wherethe three filters are mounted in a filter-wheel or filter sledge andimages are detected by one array detector.

A tristimulus image is recorded, as three separate images, by an imagecollecting and detecting means 14, here a photo detector array, throughan imaging means 15, here a lens or lens system, and through threefilters 11, 12 and 13, one for each separate image, where the threefilters are mounted in a filter-wheel or filter sledge.

FIG. 2 shows an alternative embodiment of a tristimulus filter-typeimaging camera in which three separate channels each having it own arraydetector are used. The embodiment shows three image collecting anddetecting means 14 a, 14 b and 14 c, here three CCD arrayphoto-detectors; three imaging means 15 a, 15 b and 15 c, hereillustrated by three lenses; and each channel having one of the threefilters 11, 12 and 13, here optical multilayered structures of thinfilms. This system can provide three simultaneously images.

In FIGS. 3, 4, and 5 are shown alternative arrangements of filter andimaging system.

FIGS. 3 and 4 show alternative embodiments of the present inventionshown in FIG. 1 and FIG. 2.

FIGS. 5A and 5B show alternative embodiments of an optical multilayerstructure of thin films for a calorimeter and tristimulus camera withhigh transmittance.

FIG. 6 illustrates the response folding operation for achieving filtercharacteristics of CIE colour-matching functions.

The total spectral system response is given by the CIE colour matchingfunctions {overscore (x)} (λ), {overscore (y)} (λ) and {overscore (z)}(λ) 61. The response of the filters is hence given by the residualspectral response as found by a folding procedure illustrated in FIG. 6;the transmittance of the imaging system L(λ) being found as 65, and theresponse of the image collector D(λ) being found as 64.

A computer and suitable software can control the whole process andpresent the result as images on a video display unit (VDU) or as digitalfiles.

FIG. 7 shows a tristimulus filter design by both stacking andside-by-side placement of coloured filters 71A, 71B, 71C on a substrate72 for calorimeters of the non-imaging type.

FIG. 8 shows a template for the template type calorimeter of thenon-imaging type according to prior art; said template having indicatedon top thereof the individual response functions.

FIG. 9 shows a pixel layout on a CCD chip used for colour photographywith one CCD according to prior art. FIG. 9(B) shows an enlarged sectionof the lower right corner of the CCD chip shown in FIG. 9(A).

FIG. 10 shows a layout used for colour photography with 3 CCD camerasaccording to prior art. The lens 105 and the beamsplitter 106 splits thelight into three components R, G, and B each detected by its colourdetector 104 a, 104 b, and 104 c.

FIG. 11 shows a spectral response 111, 112, 113 of RGB type CCD camerasaccording to prior art as used in FIG. 9 and 10.

FIG. 12 shows a tristimulus filter design comprising a stack of colouredfilters 112, 123, 124, and 125 for calorimeters and tristimulus cameraswith very low transmittance and medium match.

FIG. 13 shows a detailed illustration of an embodiment of a cameracomprising of a front lens group 133, next to the filters, spacing withan aperture 132 and a rear lens group 131 next to the image collectingmeans.

FIG. 14 shows measured system responses of an embodiment of a cameracompared with CIE responses. {overscore (x)}(λ), {overscore (y)}(λ) and{overscore (z)}(λ) defined by CIE are labelled 141, 142 and 143.{overscore (x)}(λ), {overscore (y)}(λ) and {overscore (z)}(λ) realisedby an embodiment of the camera is labelled 141 a, 142 a and 143 a

FIG. 15 shows a cross-sectional sketch of an integrating cavity to beused in combination with a camera according to the invention (notshown). More details are given in the examples.

FIG. 16 shows an embodiment of a camera 161 recording an image of ascene 163, and storing one or more signals representing said image in amemory 162.

The detector signals representing an image recorded by a cameraaccording to an aspect of the invention can be obtained by means knownto a skilled person. In an embodiment CCD array signals are stored in asolid-state memory, or other storage device, e.g. a DVD, CD, etc.

FIG. 17 shows an embodiment of a display 171, 172 and detector 161combination, here a camera 161 recording and storing 162 an image 163 asshown in FIG. 16, and displaying said image, optionally said storedimage, on a display 171 including suitable signal processing means 172,e.g. realized in a microprocessor or dedicated analog or digitalelectronic circuit.

Means for displaying said recorded and stored image representation,including signal processing, are known in the art, e.g. comprisingdisplay means such as an electronic display screen, preferably a videodisplay unit; a projector screen system, or an electronic printer,preferably a colour printer.

FIG. 18 shows an embodiment of a colour display 181 and a monitor system182 for monitoring a colour display, here a calibration target on amonitor screen, or the whole screen as such, and optionally correcting,or calibrating, said colour display by suitable comparator and signalcorrection means 183. The monitor 182 on-line monitors the screen of thedisplay 181 unit, said screen showing e.g. an image, and optionallyshowing a separate calibration target. A comperator and correction unit183 providing adjustment of display control signals for the display 181unit in response to said monitor control signal, whereby an optimizeddisplay, optionally corrected for drift, can be obtained.

Suitable comparator and signal correction means are known in the art,including analog and digital signal comparators, e.g. realized in amicroprocessor or dedicated analog or digital electronic circuit.

FIG. 19A shows an embodiment of a colour display 181 and monitor 182system incorporated in a display and detector combination as shown inFIG. 17 for on-line calibration of a display, e.g. a whole screen or apart thereof as shown in FIG. 19B.

The monitor 182 on-line monitors a calibration target 192 on a screen ofthe display 181 unit, said screen further showing an image 193. Acomperator and correction unit 183 providing adjustment of displaycontrol signals for the display 181 unit in response to said monitorcontrol signal, whereby an optimized display, optionally corrected fordrift, can be obtained.

Preparation of Response Adapting Filters

According to the invention said one or more response matching filters11, 12, and 13 of the filter camera are adapted to modify the spectralinformation of the radiant power from the object so that the totalresponse of the camera matches a predetermined colour-matching function(x(λ)).

In a preferred embodiment a response adapting is prepared according to amethod comprising:

-   -   providing a substrate, here exemplified by a transparent        substrate in form of a plate such as a glass plate, e.g. BG38 or        BG39;    -   coating the substrate with an anti-reflecting coating, here        exemplified by a material such as SiO₂; in a particular        embodiment said anti-reflecting coating comprises silica        deposited on directly on said substrate, e.g. in form of a glass        plate; for certain applications an anti-reflection coating is        not required on the substrate;    -   coating an optical multilayer structure, here a dielectric thin        film structure having a predetermined transmittance function        T(λ); said predetermined transmittance function being determined        by dividing the desired total response function of the camera,        here exemplified by the {overscore (x)}(λ), {overscore (y)}(λ),        and {overscore (z)}(λ) according to the CIE standard observer,        with the spectral response function of all filter components        except that of the thin film structure, the detector response        and response of the imaging system; said coating being applied        according to e.g. the technique of Sullivan et al., the major        steps of which is outlined in below;    -   applying one or more block filters onto said optical multilayer        structure, here exemplified by an absorption filter for cutting        off undesired light of wavelengths above an upper limit, e.g. IR        light above about 780 nm, and/or an absorption filter for        cutting off light having wavelength below a certain lower limit,        e.g. UV light below about 350 nm; and    -   applying one or more neutral density filters onto said one or        more block filters for attenuating the intensity of the radiant        power at all wavelengths.

Preparation of response adapting filters can be carried out in any waysuitable for achieving the desired functions for their individualapplication.

Examples of use of response adapting filters RA generally includeconfigurations: D-L-RA-A-O-S, wherein D is an image collecting anddetecting means, L is an imaging means, RA is a response adaptingfilter, A is an aperture which can be positioned elsewhere in thesystem, e.g. D-A-L-RA-O-S, D-L-A-RA-A-O-S, O is an object and S is alight source.

The response-adapting filter RA can generally include structures of thinfilms of different order, e.g. substrate-AR-T-BG-ND, subtrate-T-BG-BG,substrate-T, wherein AR is an anti-reflex coating, BG is a blockingfilter, and ND is a neutral density filter.

Preparation of Optical Multilayer Structures of Thin Films

An optical multilayer structure to be applied in a response-adaptingfilter and detector combination of the present invention can be preparedby any suitable method that allows preparation of a controlled opticalthin film structure.

Techniques include multilayer deposition techniques such as sputtering,evaporation, reactive ion-plating evaporation, and chemical vapordeposition.

Suitable thin film preparation techniques are disclosed by Sullivan etal., see e.g. “Deposition of Optical Multilayer Coatings with AutomaticError Compensation. I. Theoretical Description”, Applied Optics, Vol.31, 3821-3835, 1992, and “Deposition Error Compensation for OpticalMultilayer Coatings. II. Experimental Results—Sputtering System”,Applied Optics, Vol. 32, No. 13, 2351-2360, the content of which isincorporated herein by reference, the latter specifically including anautomated magnetron-sputtering system.

U.S. Pat. No. 6,217,720, published Apr. 17, 2001 discloses a multi-layerreactive sputtering method with reduced stabilization time fordepositing a complex multilayer coating on a substrate, said coatingconsisting of at least two materials. Optical measurements are taken ofdeposited layers and compared with model values to continually controland insurances of homogeneity of the deposited layers and allowance ofvalid thickness determination from said model. It is shown that complexfilters have been fabricated.

The system comprises:

-   -   (A) a deposition system comprising a sputtering chamber, cryo        pump, Magnetrons, etc; more details are disclosed in U.S. Pat.        No. 6,217,720, published Apr. 17, 2001, incorporated herein by        reference,    -   (B) a process control system comprising a computer controlling        chamber pressure, oxygen flow and power for the magnetrons,    -   (C) a monitoring system comprising a light source and a grating        and PDA array for retrieving spectral information, and    -   (D) a deposition control system comprising a computer        controlling the monitoring system and software for calculating        layer thickness and a possibly re-optimising of the next layer        thickness

The system is operated in a deposition sequence comprising:

-   -   (A) transfer of the multilayer design and the desired optical        performance of the coating;    -   (B) selection of process-control parameters;    -   (C) loading of substrate in deposition chamber, including        transmittance measurement of the substrate;    -   (D) establish communication between process control system and        deposition system.; and    -   (E) initiating automated deposition mode;

For each layer the following steps are performed:

-   -   (A) spectral transmission is measured and compared to the        predicted transmission;    -   (B) the refractive index and optical thickness of the previous        layer are estimated;    -   (C) the thin-film design of the non-deposited layers is        re-optimised to take into account the actual performance of the        deposited layers in the coating;    -   (D) the addition of further layers is performed as long as the        deviation between the obtained and the desired spectral        transmission exceeds a predefined level;    -   (E) the coating machine is prepared for the deposition of the        next layer, if further layers are needed. This layer is named        the present layer in the following;    -   (F) the desired optical thickness of the present layer is        estimated on basis of a re-optimisation of the theoretical        design;    -   (G) the main part of the desired thickness is deposited.        However, the layer is terminated sufficiently early that the        thickness not is too large;    -   (H) the spectral transmission is measured and compared to the        predicted transmission;    -   (I) the refractive index and optical thickness of the present        layer are estimated by comparison of the measured transmission        values and the theoretical model;    -   (J) the optical thickness of the remaining part of the present        layer is recalculated on basis of the revised spectral data;    -   (K) the deposition of the layer is finished at a reduced speed        to minimize the error in the final thickness of the layer;    -   (L) steps O to Q are repeated until a sufficient layer thickness        is obtained.

5. EXAMPLES

Preferred embodiments of the invention are illustrated by examples ofpreparation of a response-adapting filter.

Preparation of Response-Adapting Filter

Preparation of a response-adapting filter 61, here exemplified bypreparation of X, Y, and Z filters for a CIE tristimulus camera, isillustrated in FIG. 6.

The step of realising the transmittance functions T(λ,X), T(λ,Y), T(λ,Z)of the optical multilayered structure of thin films comprises:

-   -   providing a predetermined spectral-matching function 66,        generally indicated by x(λ), y(λ), z(λ), here the        colour-matching functions {overscore (x)}(λ), {overscore (y)}(λ)        and {overscore (z)}(λ);    -   measuring the spectral response function 64 of the detector,        here a common detector response D(λ) for each filter, excluding        the response of the response adapting filters;    -   measuring the spectral response function 65 of the imaging        means, here a common detector response for each filter L(λ),        excluding the response of the response adapting filters;    -   measuring the spectral response function 62 of the auxiliary        means 62, here a response function for a lens system 15 e.g. the        lens groups 131, 132, 133 shown in FIG. 13, excluding the        response of the response adapting filters;    -   measuring the spectral response function 62 of further auxiliary        means 62, here e.g. a response function for blocking filter for        blocking in g.e. The IR or/and UV region of the spectrum,        excluding the response of the response adapting filters;    -   measuring the spectral response function 62 of further auxiliary        means 62, here e.g. a response function for neutral density        filter, excluding the response of the response adapting filters;    -   generally, using the same procedure for any other auxiliary        filters, e.g. an anti-reflex filter; or substrates, including        substrates carrying said optical multilayered structure of thin        films; and    -   combining the individual responses to provide the residual        response in the transmittance functions of the optical        multilayered structure of thin films to match the desired        response of the response adapting filter.

Alternatively, the transmittance functions T(λ,X), T(λ,Y), T(λ,Z) may bederived from any suitable combination of the combined elements of thefilter, excluding the response of the response adapting filters, andthen add the residual response in the transmittance functions of theoptical multilayered structure of thin films to match the desiredresponse of the response adapting filter.

The preferred embodiment of the filters is shown in FIG. 5. Thealternatives AI and AII are for X and Y filter, while the BI and BII arefor the Z filter. The layer 51 illustrates a blue glass absorption-typefilter for blocking infrared radiation. The used types for the X and Yfilters are BG39 from Schott Glaswerke. For the Z filter is used a BG38,also from Schott Glaswerke. The layer 52 illustrates a glass substratelike BK7 from Schott Glaswerke. The layer 53 illustrates a neutraldensity filter, either a ND25, Hoya for the Y filter or a ND40, Hoya forthe X filter.

The neutral density filter types are chosen so that the total systemresponse in the X, Y and Z channels is close to even for the threechannels when exposed either to direct tungsten light or directdaylight. This gives the advantages that the three exposures can beperformed without changing anything in the camera settings, and therebyreducing time between exposures, give the same conditions for the threechannels and a good signal to noise ratio.

Even for a camera with three channels, each channel comprising a neutraldensity filter, it can be an advantages to exclude the ND filters, e.g.in order to provide desired sensitivities.

For type-I-filters with substrates 52 there is a minimum of waste ofexpensive BG glass types. The substrates are first AR coated, which is asimple process compared to the next coating process, the responseadapting coating. Then the substrates are cemented to the BG glass andoptionally the ND glass. If the coating processes did not succeed thenonly the simple substrate was wasted. This type I has though theadvantages that the thin film always is cemented against another glassand thereby protected from the moisture in the environment.

It can be difficult to cement three filters together without introducingerrors in alignment. This problem is gone when the type II filters areused, where the coatings are performed directly on the BG type glass.

This type II filters do expose the thin film to the environment, andtherefore this type should only be used for very dense coatings,resistible against moisture or in closed systems protected againstvariation in humidity.

Thin film coatings show a spectral dependency on the angle of incidence.Therefore, in this embodiment of the inventions, the response adaptingfilters are placed in front of the lens, and further the lens isselected so that the angle of view is restricted to ±10°. Further theresponse adapting filters are optimised to an angle of incidence of ±3°,hereby minimizing the overall error.

Due to tolerances in all the components, a deviation from the perfectsystem response must be expected. Therefore the image collecting system,typically comprising a PC with suitable software, can introduce acorrection procedure in form of correction matrices as mentioned forformula (7). If necessary different corrections matrices can beimplemented for the different part of the image, depending on the anglein the viewing field.

The chromatic coordinates, calculated according the formula (6) isindependent of the absolute level of light. To introduce absolutemeasurements, of luminance or Y from formula (2), the iris aperture 132,see FIG. 13, of the lens must be replaced by an aperture comprising ahole of well-known diameter. A collection of holes can be realized on awheel, and shifted in between the front 133 and rear 131 lens group,according to light level. Further, the focus distance, and shutterspeed, must be known, but with a motor driven focus system, withfeedback this is simply realized. With an embodiment as here mentioned,the tristimulus camera can be absolute calibrated to luminance andcolour measurements.

Preferred embodiments of the invention are further illustrated byexamples of production of a camera including a B/W video camera fromSONY (XCD-X700) as image collectors, and the front and rear lens groupof an objective supplied from Schneider Kreuznach (Xenoplan 1,4/23) asimaging system. A hole aperture wheel or sledge for controlling thelight level on the above-mentioned video camera was provided by meansknown to the skilled person.

Further, three response-adapting filters according to the invention wereprovided at outlined above, and mounted in a filter wheel or sledgeplaced in front of the objective for holding and shifting the filters.

Colour Measurements

As preparation for colour measurements, the tristimulus camera isexposed to complete darkness and an image (an average of say 100 image)is recorded, as the ‘dark image’ so the dark noise pattern is known.Then the camera is exposed to a known scene, preferable a uniformilluminated surface. An image (an average of say 100 image) through oneof the filters is recorded as the ‘white image’.

A colour measurement is then performed by taking one dark image,calculating the current dark level, scale the previous dark image to thecurrent dark level and hereby produce the current absolute dark noisepattern.

Then the X filter is shifted in front of the lens and first one image istaken to remove so called lag. Then a number, one ore more by choice, ofimages are averaged and the current absolute dark noise pattern issubtracted (pixel by pixel). The result is multiplied by the reciprocalwhite image (pixel by pixel). Same procedure is followed to obtain the Yand Z images.

A matrix, and a factor for scaling the images to absolute values(luminance) then correct the images.

Images can be recorded of scenes with controlled lighting conditions. Apreferred embodiment is shown in FIG. 15.

Most calibration laboratories for measuring the reflection properties ofmaterials use this set up. The integrating sphere 151 provides bothindirect and diffuse light and a shield from unwanted light. The lightis provided by light sources 152 inside the sphere or light transportedinto the sphere by example light guides. The latter has the advantagesof reducing heat problems.

A shield 153 prevents the target and the camera from receiving directlight. The target 154 is placed against an opening 157 in the sphere.The camera is measuring through another opening 155. Preferably themeasurement is done at an angle 158 towards the target, different from0°, to avoid reflections between the camera and the target. If the port156 is closed the measurement is with the specular component included,and if the port is open an equipped with a light trap, the measurementis without the specular component.

These integrating spheres are purchased from Porschke or LMT, bothGermany.

This set up is normally used to measure homogeneity of targets withnon-imaging spectroradiometers. Samples with colour textures can bemeasured with the camera and the characteristics of the texture can bemeasured and calculated. Examples are textiles and all kind of granularmaterials.

As the camera is measuring colour as the human eye, the camera is verysuitable for sorting material like marble and wood, production controletc.

Further this camera has potential in automatic screening of medicalsamples and growth in titre plates, telemedicine etc.

1. A combination of a response adapting filter and a detector, thedetector having a predetermined spectral response function (D(λ)) toelectromagnetic radiation; the response adapting filter comprising: oneor more optical multilayered structures of thin films on a substrate,said optical multilayer structures comprising two or more layers of thinfilm materials, said thin film materials comprising dielectricmaterials, metallic materials, or a combination thereof; and said layersof thin films being adapted to provide a spectral transmittance (T(λ))so that the spectral response (D(λ)T(λ)) of the detector matches apredetermined spectral-matching function (y(λ)).
 2. The combinationaccording to claim 1 comprising one or more auxiliary filters, saidauxiliary filters each having a spectral transmittance (B(λ)) of saidelectromagnetic radiation; said layers of thin films being adapted toprovide a spectral transmittance (T(λ)) so that said spectral response(D(λ)T(λ)B(λ)) of the detector, including said spectral transmittancesof said auxiliary filters, matches said predetermined spectral-matchingfunction (y(λ)).
 3. The combination according to claim 2 wherein saidone or more auxiliary filters comprises filters selected from the groupconsisting of: one or more layers of anti-reflecting coating; saidanti-reflecting coating having a spectral transmittance (B(λ)=AR(λ))attenuating one or more reflections regions of the spectrum of saidelectromagnetic irradiation; one or more blocking filters, said blockingfilters having a spectral transmittance (B(λ)=BG(λ)) attenuating one ormore regions of the spectrum of said electromagnetic radiation; and oneor more neutral density filters; said neutral density filters having aspectral transmittance (B(λ)=ND(λ)) attenuating the whole spectrum ofsaid electromagnetic radiation.
 4. The combination according to any ofclaims 1-3 wherein said predetermined spectral-matching function is astandardized response function.
 5. The combination according to claim 1wherein said predetermined spectral-matching function is acolour-matching function (x(λ), y(λ) and z(λ)) of the CIE 1931 standardcolorimetric observer.
 6. The combination according to claim 1 whereinsaid predetermined spectral-matching function is a standardized actionresponse function defined by CIE, preferably an euretheine-matchingfunction, a photo-synthesis-matching function, and a billirubin-matchingfunction.
 7. A method of preparing a response adapting filter anddetector combination, the method comprising: providing a detector, saiddetector having a predetermined spectral response function (D(λ))providing a substrate; providing an optical multilayered structure onsaid substrate; said optical multilayered structure comprising two ormore layers of thin film materials, said thin film materials comprisingdielectric materials, metallic materials, or a combination thereof; saidoptical multilayered structure being adapted to 20 provide a spectraltransmittance (T(λ)) as defined in claim 1; said two or more layers ofthin film materials being provided by deposition of said thin filmmaterials by reactive gas deposition, and said deposition beingcontrolled by optical measurements.
 8. The method according to claim 7wherein said reactive gas deposition of said thin film materialscomprises reactive ion sputtering, ion beam sputtering, reactive ionplatting, reactive ion-assisted deposition, and chemical vapourdeposition, and a combination thereof.
 9. The method according to claim7 or 8 wherein said adaptation of said optical multilayered structureinclude said layers of thin films being adapted to provide a spectraltransmittance (T(λ)) so that the spectral response (D(λ)T(λ)) of thedetector matches a predetermined spectral-matching function (y(λ))within a predetermined fitness error f₁, said fitness error f₁ beingless than 30%, preferably less than 15%, most preferred less than 5%, inparticular less than 3%.
 10. The method according to claim 7 whereinsaid thin film materials comprises materials providing hard metaloxides.
 11. The method according to claim 7 wherein said hard metaloxides are selected from the group consisting of oxides of Ti, Hf, Zr,Si, Ta, Al and Y, preferably Ti0₂, Hf0₂, Zr0₂, Si0₂, Ta₂0₅, and Y₂0₃,Al₂0₃ most preferred Ti0₂ and Si0₂.
 12. A camera, the camera comprising:an aperture means adapted to control radiant power from an object; oneor more response adapting filters as defined in claim 1, or obtainableby the method as defined in claim 7; an imaging means adapted togenerate an image of said radiant power of said object; said imagingmeans having an imaging spectral transmittance (L(λ)) and beingpositioned so that said one or more response adapting filters lie in theobject space thereof, and one or more energy collecting and detectingmeans adapted to collect and detect radiant power in discrete points ofsaid image, said energy collecting means having an image collectingspectral response (D(λ)) which is substantially similar for all saiddiscrete points of said image, said one or more response adapting filterbeing positioned in the object space of said imaging means.
 13. Thecamera according to claim 12 wherein said one or more image collectingand detecting means comprises an array of monochromatic detectors. 14.The camera according to claim 12 or 13 comprising three responseadapting filters (X,Y,Z) for each of the tristimulus colour-matchingfunctions x(λ), y(λ) and z(λ) of the CIE 1931 standard calorimetricobserver (either 2° or 10°).
 15. The camera according to claim 12wherein said one or more response adapting filter are positioned in theobject space of said imaging means within a threshold view anglethereof, said threshold angle being less than ±15 degrees, preferablyless than ±10 degrees; in particular in the range of ±5 to ±10 degrees.16. The camera according to claim 12 wherein said imaging meanscomprises an objective, said objective being adapted to provide amaximum view angle of less than ±15 degrees.
 17. The camera according toclaim 12 wherein transmission of the three filters are adjusted so thatthe imaging device can operate with constant aperture and constantintegration time and still utilise the full dynamic range of the imagingdevice.
 18. The camera according to claim 12 wherein said imagecollecting means comprises an array of photo-detectors.
 19. The cameraaccording to claim 12 wherein said aperture means comprises a movableaperture, including an aperture wheel having one or more apertures ofpredefined aperture openings.
 20. (canceled)
 21. (canceled) 22.(canceled)
 23. (canceled)
 24. (canceled)
 25. A display and detectorcombination, said combination comprising: a combination of a responseadapting filter and a detector as defined in claim 1, said combinationproducing a detector signal in response to electromagnetic radiation;and a display means, said display means comprising light emitting meansto emit light in response to said detector signal.
 26. The combinationaccording to claim 25 wherein said a combination of a response adaptingfilter and a detector as defined in claim 1 is incorporated in a cameraas defined in claim
 12. 27. The combination according to claim 25further comprising a storage means for storing said detector signals.28. The combination according to claim 25 wherein said display meanscomprises an electronic display screen, a projector screen system, or anelectronic printer.
 29. The combination according to claim 28 whereinsaid projector screen system comprises a video display unit for emittinglight in response to said detector signal.
 30. A method of displayingoptical information, said method comprising: producing a detector signalin response to electromagnetic radiation, said detector signal beingproduced by a combination of a response adapting filter and a detectoras defined in claim 1; and producing a display on a display means, saiddisplay means comprising light emitting means emitting light in responseto said detector signal.
 31. A method according to claim 30 wherein saidoptical information is a colour.
 32. A method according to claim 30wherein said optical information is an image.
 33. A colour display andmonitor system, said display and monitor system comprising: a displaymeans, said display means comprising light emitting means to emitcoloured light in response to a display control signal; and a monitormeans, said monitor means comprising a combination of a responseadapting filter and a detector as defined in claim 1, said monitor meansproducing a monitor signal in response to said emitted light of saiddisplay means.
 34. The system according to claim 33, said system furthercomprising signal storage means, said signal storage means storing atleast one reference display control signal.
 35. The system according toclaim 34 wherein said at least one reference display control signal isderived from a detector signal generated by a display and detectorcombination as defined in claims 25-29.
 36. The system according toclaim 33 wherein said at least one reference display control signal isderived from a said monitor signal.
 37. The system according to claim33, said system further comprising a signal comparator means forcomparing said monitor signal and said at least one reference displaycontrol signal, said signal comparator means producing a comparatorcontrol signal in response thereto.
 38. The system according to claim33, said system further comprising a control means for adjusting saidsaid display control signal, said control means adjusting said displaycontrol signal in response to said comparator control signal.
 39. Thesystem according to claim 33 wherein said display control signal, saidmonitor signal, said at least one reference display control signal, or acombination thereof, comprises an electronic tristimulus signal.
 40. Thesystem according to claim 33 wherein said display means comprises adisplay means as defined in claim
 25. 41. The system according to claim33 further comprising a connection means for connecting said monitorsignal to a display and detector combination as defined in claim
 25. 42.A method of controlling a colour display, said method comprising:displaying a colour on a display means, said display means comprisinglight emitting means to emit coloured light in response to a displaycontrol signal; monitoring said display means by a monitor meanscomprising a combination of a response adapting filter and a detector asdefined in claim 1, said monitor means producing a monitor signal inresponse to said emitted light of said display means; comparing said atleast one reference control signal and said monitor signal by comparatormeans for comparing said at least one reference control signal and saidmonitor signal, said comparator means producing a comparator controlsignal in response thereto; and adjusting said display control signal bya control means for adjusting said display control signal, said controlmeans adjusting said display control signal to produce a an adjustedresponse of said emitted coloured light on said display means.
 43. Themethod according to claim 42 wherein said display control signal, saidmonitor signal, said at least one reference display control signal, or acombination thereof, comprises an electronic tristimulus signal.
 44. Thecamera according to claim 12, wherein said array of monochromaticdetectors is an array of photo detectors.
 45. The combination accordingto claim 25 wherein said electronic display screen is a video displayunit.
 46. The combination according to claim 25 wherein said electronicprinter is a color printer.